The presence server manages the application types that individuals can use and their use state as presence information (e.g., JP-A Nos. 72485/2004 and 70752/2004). Communication means available to users have diversified and it has become possible for one user to use plural application at the same time. To cope with such a situation, users' presence information includes three elements: (1) user name, (2) the type of application used by user, and (3) states of individual applications.
Individual applications operate independently, and when a user activates an application, the user registers the state of the application as “idle” in a presence server. Many of the application with presence information establish a session with a communication party, and perform data transmitting/receiving within the session. The state of being in communication exists in the applications, and the state of the applications is registered as “in communication” when the session is established. One user does not communicate at the same time with plural counter parties, and a session is always established with a one-to-one relationship with the user. When the user is in communication with a specific counter party, it does not establish a session with another user. Therefore, if the user acquires presence information of a counter party that is usable, the user establishes a session to perform communications. However, if the presence information of the counter party indicates “in communication”, the user waits until the communication of the counter party terminates.